Devices such as wireless devices are also known as e.g. User Equipments (UE), mobile terminals, wireless terminals and/or mobile stations. Devices are enabled to communicate wirelessly in a wireless communications system or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two devices, between a device and a regular telephone and/or between a device and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the wireless communications system.
Devices may further be referred to as mobile telephones, cellular telephones, or laptops with wireless capability, just to mention some further examples. The devices in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as device or a server.
The wireless communications system covers a geographical area which is divided into cell areas, wherein each cell area being served by a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the devices within range of the base stations.
In some RANs, several base stations may be connected, e.g. by landlines or microwave, to a radio network controller, e.g. a Radio Network Controller (RNC) in Universal Mobile Telecommunications System (UMTS), and/or to each other. The radio network controller, also sometimes termed a Base Station Controller (BSC) e.g. in GSM, may supervise and coordinate various activities of the plural base stations connected thereto. GSM is an abbreviation for Global System for Mobile Communications (originally: Groupe Spécial Mobile).
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
UMTS is a third generation mobile communication system, which evolved from the GSM, and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UMTS Terrestrial Radio Access Network (UTRAN) is essentially a radio access network using wideband code division multiple access for devices. The 3GPP has undertaken to evolve further the UTRAN and GSM based radio access network technologies.
According to 3GPP GSM EDGE Radio Access Network (GERAN), a device has a multi-slot class, which determines the maximum transfer rate in the uplink and downlink direction. EDGE is an abbreviation for Enhanced Data rates for GSM Evolution. In the end of 2008 the first release, Release 8, of the 3GPP Long Term Evolution (LTE) standard was finalized and later releases have also been finalized.
Recent developments of the 3GPP LTE facilitate accessing local Internet Protocol (IP) based services in the home, office, public hot spot or even outdoor environments. One of the important use cases for the local IP access and local connectivity involves the direct communication between devices in close proximity, typically less than a few 10s of meters, but sometimes up to a few hundred meters of each other.
In network-controlled so-called Device-to-Device (D2D) communications, a network such as a radio access network assists wireless devices that are in the proximity of each other to discover one another. This process is referred to as device discovery. The wireless devices may then establish a direct link referred to as D2D bearer establishment, rather than a link via the base station. In fact, when two devices communicate with each other via a cellular base station, the communication path involves an uplink hop and a downlink hop. Both of these hops have associated resources, as opposed to the single hop direct D2D link. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the wireless device. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the wireless device to the base station.
The initiation of the establishment of the D2D link may be made by the radio access network or by any of the wireless devices of the D2D pair. In network initiated D2D link establishment, the network realizes that two communicating wireless devices are in proximity of each other. In device initiated D2D link establishment, the wireless devices discover the proximity of each other and also some of their capabilities which is necessary for them to establish a D2D link, similar to Bluetooth.
In network-controlled D2D communication, a network control function performs at least one of: a) provisioning of a discovery signal to be used between two devices to determine their proximity and/or D2D link estimation, b) resource assignment for the D2D discovery signal and/or a D2D data channel and/or a D2D control channel, c) relaying of information between the at least two devices, and d) configuration of connection parameters for the at least two devices of the D2D link, such as power setting, e.g., actual, min, max, coding and modulation schemes, segmentation configuration, e.g., transport block sizes, parameters and/or security keys for encryption/integrity protection and protocol parameters.
A transmission in an LTE or Evolved Universal Terrestrial Radio Access Network (E-UTRAN) is based on Orthogonal Frequency Division Multiplexing (OFDM), whose format may be modeled as an OFDM time-frequency grid. The OFDM time-frequency grid is comprised in one axis of frequency values and in the other axis of time. The frequency axis is subdivided in a number of frequency sub-carriers, with a spacing that may typically correspond to 15 kHz, while the time axis is subdivided in OFDM symbol intervals.
Within the grid, a Physical Resource Block (PRB or RB) is a unit of transmission resource consisting of twelve consecutive sub-carriers in the frequency domain and one time slot, 0.5 ms, in the time domain.
The direct communication mode, or D2D communication, enables a number of potential gains over the traditional cellular technique, because D2D devices are much closer to one another than cellular devices that have to communicate via a cellular access point, e.g., a base station:
Capacity gain: First, radio resources, e.g., OFDM RB, between the D2D and cellular layers may be reused, i.e., reuse gain. Second, a D2D link uses a single hop between the transmitter and receiver points as opposed to the 2-hop link via a cellular access point, i.e., hop gain.
Peak rate gain: due to the proximity and potentially favorable propagation conditions, modulation and coding scheme (MCS) of higher order may be applied, so that, the maximum achievable data rate may be further improved, i.e., proximity gain;
Latency gain: When the devices communicate over a direct link, the base station forwarding is short cut and the end-to-end latency may decrease.
According to the current LTE protocol, a network node exerts control over signalling of wireless devices in a wireless communications network through, for example, Radio Resource Control (RRC) signalling. There are two types of RRC signalling: broadcast signalling, e.g., System Information Block/Master Information Block (SIB/MIB), and device dedicated signalling. In turn, the wireless devices in the network feed back to the network node signalling through HARQ signalling in order to acknowledge the correct reception of signalling through an ACKnowledgement (ACK) or the incorrect reception of the signalling via a Negative ACKnowledgement (NACK), which then leads to a request for retransmission of the improperly received signalling. In particular, the wireless device may feedback with an Acknowledgement/Negative Acknowledgement (ACK/NACK) on the Uplink (UL) Physical Uplink Control CHannel (PUCCH). Since the content of the HARQ signalling is obviously dependent on the reception of a specific wireless device, broadcast signalling, which is signalled to multiple devices, is not suitable to carry this type of signalling. Dedicated signalling, on the other hand, is better suited of the HARQ signalling because it is intended for a specific device.
However, current specifications such as the current LTE protocol, do not provide an optimized performance of the control and HARQ signalling processes for D2D communications.